Ceramic tile and method for manufacturing ceramic tiles

ABSTRACT

Ceramic tile having a ceramic base layer and a cover glaze layer including a printed pattern, where the surface of the ceramic tile has a relief having structural features corresponding to the printed pattern. The structural features are at least partly formed in the surface of the ceramic base layer and manifest themselves through the glaze layer to the upper surface of the tile. Additionally, a method which allows for the manufacturing of such ceramic tiles.

The present invention relates to ceramic tiles and a method ofmanufacturing ceramic tiles.

The invention is in particular concerned with ceramic tiles having aceramic base layer and a cover glaze layer comprising a printed pattern.

BACKGROUND

Such ceramic tiles are well known. ES 2 196 991 describes a method ofmanufacturing ceramic tiles wherein the pattern is printed by means ofscreen printing or rotary serigraphy. EP 1 038 689 describes a digitalprinting technique for decoration of ceramic tiles, for example with amarble motif, in which a multicolor printing is effected in a singlepass of the tile underneath a plurality of printing modules. Theprinting is effected before a first baking or between successivebakings. Although intricate patterns can be created with thesetechniques, the obtained surface of the ceramic tile is monotonous. CN103241049 A shows an example of the intricacy that can be obtained withmarble motifs.

CN 203080849 U describes an equipment for producing a full polishedglaze porcelain tile. This equipment comprises a green brick processingequipment for producing a ceramic base layer, a cover glaze layer issprayed and an pattern may be printed using an inkjet printingequipment. The equipment further comprises a kiln for firing the tiles.

From DE 31 13 661 A1 it is known to provide the ceramic base layer witha chamfered perimeter. From GB 1 320 637 it is known to provide asurface of a tile with a relief. The tiles from these documents do notfeature prints, the obtained relief is rather coarse and each tilefeatures an identical relief. Such technique, in particular such relief,is hence not suited for ceramic tiles that imitate natural products suchas wood and stone.

U.S. Pat. No. 8,507,098 and BE 1019265 describe examples of glaze layersapplied to ceramic base layers and methods of applying glaze. In thesecases it concerns basically so-called dry glazes. JP 3-150283 disclosesdry as well as wet glazes for ceramic tiles, wherein a smooth surface ofthe cover glaze layer is obtained after a pressing operation.

Ceramic tiles having a printed pattern showing a wood grain are known aswell. Such tiles often have a rectangular and oblong shape with thegrain lines running substantially in a longitudinal direction. Therelief provided on the surface of such tiles, if any at all, is coarseand appears artificial. When no relief is applied, or only random relieffeatures, the tiles may look glossy when viewed against light, andappear as a white surface due to the mirror-like light reflection on theglaze layer.

Ceramic tiles of rectangular and oblong shape bring about problems ininstallation. Such ceramic tiles may be somewhat domed and laying thetiles next to each other in an offset relationship creates heightdifferences which are clearly noticeable especially when viewed againstthe light. An offset relationship between installed tiles in adjacentrows is especially desirable where the tiles have a printed patternshowing a wood grain.

SUMMARY Of THE INVENTION

The present invention in the first place aims at an alternative ceramictile, which, in accordance with its several preferred embodiments, couldoffer a solution to one or more problems with the tiles of the state ofthe art. Therefore, the invention concerns a ceramic tile having aceramic base layer and a cover glaze layer comprising a printed pattern,with the characteristic that the surface of the ceramic tile comprises arelief having structural features corresponding to said printed pattern.In other words, the ceramic tile is characterized by the fact that oneor more relief features are positioned in a fixed relation to a featureof the printed pattern. E.g. the relief feature may coincide with aprinted feature, follow a printed feature or be positioned at a defineddistance to a relief feature. The correspondence between certain relieffeatures and the printed pattern leads to a less artificial impressionof the ceramic tile.

The invention is especially interesting in an installation where oblongrectangular tiles of adjacent rows are present in an offsetrelationship. The possible height differences originating from adjacentoffset domed tiles may appear less prominent when viewed against light,since the irregular surface will reflect the falling-in light morediffuse. Furthermore, the attention of the viewer will be distracted bythe intricate relief features.

According to an important preferred embodiment of the inventionirregular or random relief features distributed over the entirety of thesurface of the ceramic tile, or essentially over the entirety of thesurface of the ceramic tile, are combined with the structural featuresthat correspond to the printed pattern. An optimum counteraction ofmirror-like reflection of light may be achieved with this preferredembodiment. Preferably the irregular or random relief features define anaverage depth or height which is smaller than the average depth orheight of the structural relief features that correspond to the printedpattern. It is noted that the average depth or height of these featuresmay be recorded using techniques similar to those commonly used in thearea of surface roughness measurements, in particular similar to thoseused for defining the Ra-values of a roughness profile, namely byrecording and calculating the arithmetic average of absolute deviationfrom an average plane. Preferably such irregular or random relieffeatures define an Ra value of at least 10 micron, but is preferablyhigher, namely around 25 micron or more, or even around 50 micron ormore.

The structural features that correspond to the printed patternpreferably have an average depth or height of at least 100 micron, oreven better at least 250 micron.

Preferably, said relief is basically formed as a plurality ofexcavations present in the generally plane upper surface of the ceramictile.

Preferably said printed pattern and/or said relief extends substantiallyover the entire surface of the ceramic tile. It is clear that thestructural relief features that correspond to the printed pattern areavailable throughout the surface of the ceramic tile, without coveringthe entire surface of the ceramic tile, while the above mentionedoptional irregular or random features preferably do cover the entiresurface of the ceramic tile. When imitating a wood material, wood grainimitating structural relief features are available in accordance withall available printed wood grain lines, while in between the printedwood grain lines such structural relief features are not available.Instead, in between the printed wood grain lines the aforementionedirregular or random relief features may be available.

Preferably, said printed pattern represents a wood or stone pattern,preferably representing only one one-piece wooden plank or stone tileover the entire surface of the ceramic tile.

According to a preferred embodiment, said printed pattern is a woodpattern and said structural features are lines following the course ofthe grain lines of the wood pattern and/or a plurality of successivedashes having a configuration following the grain lines of the woodpattern.

Said structural features may be formed in the surface of the ceramicbase layer and manifest themselves through the glaze layer to the uppersurface of the tile. However, preferably said structural features have adepth such that they are substantially or completely situated above saidceramic base layer. Such structural features can be made less coarse.

Preferably, said cover glaze layer at least comprises a glaze layer ofuniform color arranged underneath said printed pattern, preferably ofwhite, beige or grey color. Such glaze layer may hide imperfections inthe surface of the ceramic base layer. The use of glazes of a colorother than white may lead to a lowering of the needed ink lay-up forobtaining the desired colors in the printed pattern.

Preferably, said cover glaze layer is obtained at least partially from aso-called wet glaze. In the most preferred embodiment, said structuralfeatures are formed in the surface of the ceramic base layer and thestructured surface of the ceramic base layer is provided with a wetapplied glaze layer. A wet applied glaze layer is preferred because ofits power to copy the structure of the ceramic base layer at its ownsurface. Such wet glaze layer preferably relates to an aqueoussuspension of at least silica or SiO2, preferably in a quantity higherthan 20 percent dry weight of the suspension and even more preferablebetween 30 and 75 percent dry weight. Preferably the suspension alsocomprises a flux component for lowering the melting temperature of theglaze. It is of course not excluded that said cover glaze layer would beobtained at least partially from a so-called dry glaze. In such case,the dry glaze is preferably made up from particles having an averageparticle size of 500 micron or lower. Preferably the average particlesize is between 200 and 400 micron.

According to a special embodiment, said cover glaze layer at leastcomprises a transparent glaze layer arranged over said printed pattern.In such case at least some or all of said structural features may beformed in said transparent glaze layer, e.g. with a depth such that theyare substantially or completed located above the print layer.

According to another special embodiment which may or may not be combinedwith the above embodiments, said cover glaze layer possesses or isformed to have an irregular texture which functions as theaforementioned irregular or random relief features distributed over thesurface of the ceramic tile.

Preferably, said printed pattern is a digitally printed pattern, and ispreferably formed at least from the base colors cyan, magenta, yellowand black. Such printed pattern may be applied using a device similar tothe one disclosed in EP 1 038 689, namely a single pass inkjet printer,wherein each tile is printed separately with a single pass of therespective tile underneath the fixed print heads of the device.

The most preferred embodiment of the present invention relates to aceramic tile that is rectangular and oblong, wherein the cover glazelayer comprises a printed wood pattern with the grain lines runningsubstantially in the longitudinal direction of the tile. The structuralfeatures in the surface of the tile follow the course of the printedgrain lines. In between these structural features irregular or randomrelief may be available over the entirety or about the entirety of thesurface of the tile.

Preferably, the ceramic tile of the invention, and in particular saidcover glaze layer, has an abrasion resistance of at least Class 2, butpreferably of Class 3 or higher, as measured according to ASTM C1027-99.

The invention also relates to a ceramic floor or a package comprising aplurality of tiles with mutually different printed patterns andcorresponding structural features, in accordance with the abovedescribed invention. When the printed pattern is digitally achieved, itcan conveniently be exchanged for another pattern, such that tiles withmutually different printed patterns are achieved. Preferably, also therelief is adapted such that the structural features of the new reliefmatches the new printed pattern. Preferably at least six or eightdifferent tiles are produced. In such case a ceramic floor assembledfrom such tiles will profit from a natural look with convincing nuances.

The invention further relates to a method for manufacturing ceramictiles, which could also be used for manufacturing the tiles of thepresent invention. Therefor the invention concerns a method formanufacturing a ceramic tile, wherein said ceramic tile has a ceramicbase layer and a cover glaze layer with a printed pattern, and whereinthe method comprises the following steps:

-   -   the step of forming the ceramic base layer;    -   the step of providing a glaze layer on said ceramic base layer;    -   the step of printing a pattern on said glaze layer;    -   the step of firing the ceramic base layer with the glaze layer        having the printed pattern;

with the characteristic that the method further comprises the step offorming a relief having structural features corresponding to saidprinted pattern. It is clear that the obtained tile preferably shows thecharacteristics of the previously described ceramic tile of theinvention. Preferably, said relief is basically formed as a plurality ofexcavations present in the generally plane and/or irregularly structuredupper surface of the ceramic tile.

The relief can be obtained at several locations or instances during theprocess of manufacturing the tile. A non-exhaustive list ofpossibilities according to which the method of the invention can be putinto practice are listed here below.

According to a first possibility, said relief is formed on the surfaceof said cover glaze layer before said step of firing and/or at the sametime as said step of firing. Preferably said relief is achieved by meansof a structured press element, such as a structured roller or astructured plate. When used during firing, said press element ispreferably made from a ceramic material, such that it can withstand thefiring temperatures, which preferably reach a maximum of at least 1000degrees centigrade. When used exclusively before firing, said presselement may be made from a metallic or a plastic material, like athermosetting melamine based material or a silicone based material orsimilar.

Preferably each tile, or limited number of tiles, e.g. maximum four, hasits own structured press element associated to it. In order to reach anacceptable number of different surface textures, each of them comprisingfeatures which are in accordance with the printed pattern, preferablydifferently structured press elements should be used. Preferably tileswith at least six or eight different surface textures are obtained fromthis first possible method of the invention.

In accordance with this first possibility, the ceramic tiles preferablyalready are provided with said printed pattern before said relief isbeing formed, such that printing may take place on a still flat glazesurface. In such case the printed pattern may be applied with anyprinting technique, such as with rollers, or with a digital printer,such as with an inkjet printer. To make sure the right surface textureor relief is applied to each tile, such that corresponding structuralfeatures are obtained, the method of the invention preferably contains astep of detecting the printed pattern, either directly or indirectly.With “directly” is meant that the actual print is recorded, e.g. withcamera's or other sensors, and identified, such that the suitable presselement can be selected to go with the tile, or a limited number oftiles. With “indirectly” is meant that tile is identified using thedetection of a feature other than the print itself, but which is in aone-on-one relation to the printed pattern, e.g. a marking applied tothe bottom of the tile. It is not excluded that the print would only beapplied to the tile after the surface of the tile had already beenprovided with a relief. In such case preferably a non-contact printingprocess is used for realizing the printed pattern, such as a processusing an inkjet printer. As an alternative, a contact printing processmay be used, e.g. a process in which a roller printer having relativelysoft, e.g. rubber rollers is applied. To make sure the right printedpattern is applied to each structured tile, such that correspondingstructural features are obtained, the method of the invention preferablycontains a step of detecting the surface structure of the tile, eitherdirectly or indirectly, such that the right print may be applied to eachtile. With “directly” and “indirectly” having similar meanings asdescribed above, but now with respect to the surface structure, insteadof the printed pattern. A direct recording of the surface structure ise.g. possible with tactile sensors or with optical scanning devices.

The structural features applied by means of said first possibilities maybe excavations in the generally plane and/or irregularly structuredupper surface of the cover glaze layer, and/or zones of different glossdegree in said upper surface. In the case of zones of different glossdegree, these preferably also correspond to parts of the printedpattern, but in accordance with a deviating variant of the inventionthey are independent of the printed pattern.

According to a second possibility, said relief is formed on the surfaceof said ceramic base layer before said step of providing a glaze layer.Preferably, said relief is obtained during the step of forming saidceramic base layer. Such ceramic base layer may be formed starting formpowder material, e.g. clay, which is pressed to form a so-called greentile, which may be dried and/or possibly fired to form a so-calledbiscuit tile. Said relief is conveniently obtained during the pressingof said powder material, for example by using a structured matrix in therespective press. Said structured matrix may be made from a metallic ora plastic material, like a thermosetting melamine based material or asilicone based material or similar.

Preferably each tile, or limited number of tiles, e.g. maximum four, hasits own structured matrix associated to it. In order to reach anacceptable number of different surface textures, each of them comprisingfeatures which are in accordance with the printed pattern, preferablydifferently structured matrices should be used. Preferably tiles with atleast six or eight different surface textures are obtained from thissecond possible method of the invention.

The common green tile presses are relatively small and press only one ora limited number of tiles at a time. Different surface textures could beachieved in several practical ways even with such small presses.According to a first possibility the structured matrix may be exchangedin between sequential pressings, preferably in an automatic way.According to a second possibility green tiles may be pressed in two ormore presses each comprising a differently structured matrix and thenfurther treated in similar ways, namely at least printed with similarprinted patterns such that they can be mixedly installed in a ceramicfloor. According to a third possibility use is made of a multiplecompartment press, such that several green tiles can be pressed andstructured simultaneously in the same press, each with its ownassociated press element or structured matrix. According to a fourthpossibility one or more green tiles may be pressed successively in aplurality of presses, each equipped with a differently structuredmatrix, such that the obtained relief is in fact a superposition of thestructures applied in successive press operations. According to anexample four presses may be in operation and each equipped with adifferently structured matrix. Each green tile is pressed either in oneof these presses or in two of these presses successively. Such anoperation would lead to ten different surface structures.

It is clear that in accordance with this second possibility of puttingthe invention into practice, the printed pattern is applied to thealready structured upper surface of the ceramic tile. To make sure thatthe right printed pattern is applied to each structured tile, such thatcorresponding structural features are obtained, the method of theinvention preferably contains a step of detecting the surface structureof the tile, either directly or indirectly, such that the right printmay be applied to each tile. As stated before, the structured uppersurface of the ceramic base layer is preferably first treated with alayer of glaze before printing takes place. The step of printingpreferably applies a digital pattern by means of an inkjet printer, butroller printers, preferably with soft or rubber rollers, are notexcluded.

According to a third possibility some relief features are made inaccordance with said second possibility, while other relief features aremade in accordance with said first possibility. Preferably the morecoarse relief features are made in accordance with said secondpossibility. For example said second possibility may be applied forforming chamfered edges to the tile, or to form imitations of flakestructures of stone, such as slate, or to imitate worn out or scrapedaway parts of wood, while said first possibility is applied for formingimitations of surface irregularities of stone or grain structure inwood. Said first possibility may also be used to form zones of differinggloss on the surface of the tile, while said second possibility is usedto form excavations on said surface.

In general, in the methods of the invention, preferably use is made of acontinuous firing unit or kiln, wherein each tile travels for,preferably 20 to 45 minutes, through a tunnel with heated and/or cooledzones. When a relief or part of the relief is being applied during thestep of firing, as may be the case in the above mentioned firstpossibility of carrying out the method of the invention, the presselement may be flat and travel along on the surface of the tile. In thecase of oblong tiles, the tiles preferably travel through the kiln intheir longitudinal direction.

It is noted that, in the case an inkjet printer is used to obtain saidprinted pattern, the change of the pattern preferably relates to achange of data to be printed. In the case a roller printer is used, thechange of the pattern preferably relates to the use of a differentroller or different sets of rollers, but may also relate to an indexingof a roller or a set of rollers, such that a different printing sectionalong the circumference of the respective roller is selected. It isnoted that the use of a different roller or set of rollers may be put topractice by replacing or exchanging the respective rollers at a rollerposition along the printing section in the production line, or byactivating and deactivating the respective rollers already present alongthe printing section in the production line. Said replacing, exchanging,activating, deactivating may be performed manually or automatically.

It is further noted that the printed pattern is preferably applied in afixed relationship to a predetermined point, such that the print isapplied at a predetermined location of the tile, e.g. at a fixeddistance, that may be zero, from an edge or corner, and that the printedpattern is preferably aligned to an edge, preferably a longitudinal edgein the case of oblong tiles. Such can be obtained through a detection ofthe upcoming tile, and using this detection to control the printer.Applying the printed pattern in a fixed relation to a predeterminedpoint is advantageous for obtaining corresponding structural features inthe relief.

It is advantageous for the correspondence between the relief and theprinted pattern when the tile is not subjected to firing operations inbetween the step of printing and the step of structuring, whichevercomes first. Preferably, the tile is not subjected to temperatureshigher than 500 degrees centigrade in between these two steps.Preferably no extra heat is applied to the tile in between these twosteps, and even better, the tile is maintained at the same temperature,which is preferably between 10 degrees and 80 degrees centigrade, forexample room temperature or about 18 to 23 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

With the intention of better showing the characteristics of theinvention, in the following, as an example without any limitativecharacter, several preferred forms of embodiments are described withreference to the accompanying drawings, wherein:

FIG. 1 represents a top view of a ceramic tile in accordance with thepresent invention;

FIG. 2, in a larger scale, represents a cross-section in accordance withline II-II indicated on FIG. 1;

FIGS. 3 in 4 in a view similar to that of FIG. 2 represent a variant.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an example of a ceramic tile 1 imitating a one piece woodenplank. The tile is rectangular and oblong with the wood graining runningsubstantially in the longitudinal direction of the tile.

FIG. 2 clarifies that the tile comprises a ceramic base layer 2, and acover glaze layer 3 having a printed pattern 4. The tile has a reliefformed by excavations 5 in its generally planar top surface. A pluralityof the excavations 5, or structural features of the relief is present inaccordance with the printed pattern 4, in this case with the darkerareas of the printed pattern 4. These excavations 5 are following thecourse of the printed wood grains.

The excavations of FIG. 2 are formed in accordance with the abovementioned first possibility for the method of the invention, whereinsaid relief is formed in the cover glaze layer before firing. As can beseen from FIG. 2 the surface of the ceramic base layer 2 stays flat, oras good as flat.

FIG. 3 gives an example where the excavations 5 are formed in accordancewith the above mentioned second possibility for the method of theinvention, wherein said relief is formed in the surface of the ceramicbase layer 2, and copied through the cover glaze layer 3.

FIG. 4 gives an example where the relief is partially formed inaccordance with said first possibility, namely the excavations 5A, andpartially formed in accordance with said second possibility, namely theexcavations 5B.

The present invention is in no way limited to the forms of embodimentdescribed by way of example and represented in the figures, however, cansuch ceramic tile and method for manufacturing be realized in variousforms and dimensions without leaving the scope of the invention, asdefined by the appended claims.

The invention claimed is:
 1. A method for manufacturing a set of ceramictiles, wherein each ceramic tile has a ceramic base layer and a coverglaze layer with a printed pattern, wherein each tile of the set has itsown printed pattern and wherein the method comprises the following stepsfor each tile of the set: the step of forming the ceramic base layer;the step of providing a glaze layer on said ceramic base layer; the stepof printing a pattern on said glaze layer; the step of firing theceramic base layer with the glaze layer having the printed pattern;wherein the method further comprises the step of forming a relief havingstructural features corresponding to said printed pattern, wherein eachtile of the set has its own surface structure texture, and wherein themethod further comprises the step of detecting the surface structure ofthe tile or the step of detecting the printed pattern.
 2. The method ofclaim 1, wherein said relief is formed as a plurality of excavationspresent in the generally plane upper surface of the ceramic tile.
 3. Themethod of claim 1, wherein said relief is formed on the surface of saidcover glaze layer before said step of firing and/or at the same time assaid step of firing.
 4. The method of claim 1, wherein said relief isformed on the surface of said ceramic base layer before said step ofproviding a glaze layer.
 5. The method of claim 1, wherein said reliefis formed on the surface of said ceramic base layer before said step ofprinting a pattern on said glaze layer.
 6. The method of claim 1,wherein said relief is formed on the surface of said ceramic base layerafter said step of printing a pattern on said glaze layer.
 7. The methodof claim 1, wherein said step of printing is a digital inkjet printingstep.
 8. A ceramic tile obtainable with the method according to claim 1,having a ceramic base layer and a cover glaze layer comprising a printedpattern, wherein the surface of the ceramic tile comprises a reliefhaving structural features corresponding to said printed pattern.
 9. Theceramic tile according to claim 8, wherein said printed pattern extendssubstantially over the entire surface of the ceramic tile.
 10. Theceramic tile according to claim 8, wherein said printed patternrepresents a wood or stone pattern, preferably representing only oneone-piece wooden plank or stone tile over the entire surface of theceramic tile.
 11. The ceramic tile according to claim 8, wherein saidprinted pattern is a wood pattern and said structural features are linesfollowing the course of the grain lines of the wood pattern or aplurality of successive dashes having a configuration following thegrain lines of the wood pattern.
 12. The ceramic tile according to claim8, wherein said structural features have a depth such that they arecompletely situated above said ceramic base layer.
 13. The ceramic tileaccording to claim 8, wherein said cover glaze layer at least comprisesa glaze layer of uniform color arranged underneath said printed pattern.14. The ceramic tile according to claim 8, wherein said cover glazelayer at least comprises a transparent glaze layer arranged over saidprinted pattern.
 15. The ceramic tile according to claim 8, wherein atleast some of said structural features are formed in said transparentglaze layer.
 16. The ceramic tile according to claim 8, wherein saidprinted pattern is a digitally printed pattern.
 17. The ceramic tileaccording to claim 8, wherein said printed pattern is formed at leastfrom the base colors cyan, magenta, yellow and black.
 18. The ceramictile according to claim 8, wherein said relief is formed as a pluralityof excavations present in the generally plane upper surface of theceramic tile.